In a transmission, particularly an automatic transmission of a motor vehicle, the pressure is regulated in a hydraulic circuit according to requirements. While for the supply of lubricating oil to the parts of the transmission, the pressure level can be kept low in a hydraulic circuit, during the shifting operations the pressure has to be sharpy raised in order, for example, to be quickly able to fill shifting elements.
According to the prior art, there have been used for regulating the pressure in hydraulic circuits pressure regulators which control shift valves for actuating the clutch. The shift valves are controlled within the pressure regulator by means of a proportional magnet consisting, among other elements, of a magnetic core, a magnetic coil and a magnetic armature. The proportional magnet controls here the coil current proportionally to an output variable force, that is, according to the coil current the magnetic armature and therewith the shift valve are controlled for actuating the clutch. From the resulting characteristic magnetic force-current characteristic lines of the pressure regulator are produced in an electrohydraulic control of automatic transmissions the pressure-current characteristic lines desired for clutch adaptation.
In the Applicant's German Patent Application DE 100 03 896 A1, a pressure regulator is described which adjusts as needed a shift valve by means of a stationary proportional magnet, a magnetic coil, a movable magnetic armature and a specific control system thus regulating the pressure in the hydraulic circuit. The pressure-current characteristic line has a curve continuously rising from the start on, that is, as the current force increases so increases the pressure also. But in the practice, the gradient of the pressure-current characteristic line is in operation too large for the requirements so that the pressure-current characteristic line is too steep and thereby the current sensitivity of the pressure regulation is not enough for a comfortable gear ratio. In case of a low load, that is, at low pressures, the low sensitivity makes itself noticeable specifically in a poor shifting quality.
Therefore, the invention is based on the problem of overcoming the disadvantages of the prior art and, in particular, of providing a proportional pressure-regulator valve for regulating a pressure level in a hydraulic circuit and of outlining a method by which the changes of pressure level in a hydraulic circuit are adjusted to be as comfortable as possible and showing how such a proportional pressure-regulator valve is controlled.
The problem on which the invention is based is solved by a proportional pressure-regulator valve and a method of regulating a pressure level in a hydraulic circuit with a proportional pressure-regulating valve.